Rolling regeneration diesel particulate trap

ABSTRACT

A rolling regeneration diesel particulate filter and filtering process that utilizes NO produced in the process to generate additional amounts of NO 2  than the NO 2  produced by the diesel engine. The process includes the step of flowing diesel engine combustion exhaust through a filter system including a first section and a second section. The first section is positioned upstream of the second section with respect to the direction of the flow of the diesel engine exhaust through the filter. The first section includes a foam constructed and arranged to trap carbon-based particulates in the exhaust. A first catalyst is carried by the foam to promote the conversion of NO in the exhaust from the diesel engine to NO 2 . The first catalyst also promotes the reaction of NO 2  with at least a portion of the carbon-based particulates trapped by the foam to form CO and NO. The first catalyst carried by the foam also promotes the oxidation of CO to CO 2 , and the oxidation of NO, generated by the reaction of NO 2  with carbon, to generate additional amounts of NO 2 . The additional amounts of NO 2  are also utilized to oxidize the carbon-based particulates. The second section of the filter system includes a wall flow monolith having a plurality of through hole cells formed therein running the longitudinal length of the monolith. The monolith is constructed and arranged to trap particulates in the exhaust and to promote the reaction of NO 2  and carbon to produce NO and CO. The ceramic foam may also be received in and surrounded by the wall flow filter.

TECHNICAL FIELD

[0001] This invention relates to filter systems, and more particularlyto a filter system for a diesel engine utilizing a rolling regenerationdiesel particulate trap.

BACKGROUND OF THE INVENTION

[0002]FIG. 1 illustrates a prior art filter system 10 for a dieselengine 12. An exhaust line 14 is provided between the diesel engine 12and the filter system 10. The filter system may include a housing 16that includes at least a first section 18 and a second section 20. Thefirst section 18 typically includes a flow-through monolith 22 thereinand wherein the flow-through monolith is coated with a catalyst such asplatinum. The exhaust gas from the diesel engine 12 includes a varietyof constituents including NO and particulate matter which typically isin the form of a carbon-based material. The catalyst on the flow-throughmonolith 22 promotes the reaction of the NO with oxygen also present inthe exhaust gas to form NO₂. However, the reaction is not efficientenough to completely convert all of the NO in the exhaust gas to NO₂.Thus, as shown in FIG. 1, both NO and NO₂ leave the first section 18 ofthe filter and enter the second section 20 of the filter system. Thesecond section 20 typically includes a wall flow monolith 24 therein.Wall flow monoliths are known to those skilled in the art and typicallyare manufactured from a ceramic material in a manner to provide aplurality of through hole cells running the longitudinal length of themonolith. The cross-sectional area of these through hole cells isextremely small, on the order of 10 microns. Wall flow monoliths arecapable of trapping 99+ percent of the particulate emissions from adiesel engine. However, wall flow monoliths can become plugged veryeasily due to the very small openings of the through hole cells. Asshown in FIG. 1, NO₂ in the exhaust gas can be used to oxidize thecarbon to form NO and CO, thus removing some of the particulate blockingthe wall flow monolith. However, the amount of NO₂ present in theexhaust gas from the diesel engine or generated in the flow-throughmonolith 22 may not be sufficient to completely oxidize the particulateblocking the wall flow monolith. Accordingly, the engine must beoperated in order to generate substantial amounts of NO₂ necessary tooxidize all the carbon and other particulate matter blocking the wallflow monolith. Otherwise, the wall flow monolith must be cleaned inanother fashion.

[0003] Thus, it would be desirable to provide a filter system for adiesel engine which resulted in the wall flow monolith being pluggedless often and providing an alternative means for regenerating the trap.The present invention overcomes deficiencies in the prior art andprovides alternatives and advantages thereto.

SUMMARY OF THE INVENTION

[0004] The invention includes a rolling regeneration diesel particulatefilter and filtering process that reuses NO produced in the process togenerate additional amounts of NO₂. One embodiment of the inventionincludes a process including flowing diesel engine combustion exhaustthrough a filter system including a first and a second section. Thefirst section is positioned upstream of the second section with respectto the flow direction of the exhaust. The first section includes a foamconstructed and arranged to trap carbon-based particulates in theexhaust. A first catalyst is carried by the foam to promote theconversion of NO in the exhaust from the diesel engine to NO₂. The NO₂is used to oxidize particulates trapped by the foam to form CO and NO.The first catalyst or a second catalyst on the foam further promotes theoxidation of CO to CO₂, and the oxidation of NO, generated by thereaction of NO₂ with carbon, to generate additional NO₂. The secondsection of the filter system includes a wall flow filter having aplurality of through hole cells formed therein running the longitudinallength of the wall flow filter. The wall flow filter is constructed andarranged to trap particulates in the exhaust and to promote the reactionof NO₂ and carbon to produce NO and CO.

[0005] In another embodiment of the invention, the foam may include aceramic foam made from Al₂O₃.

[0006] In another embodiment of the invention, the ceramic foam may alsoinclude ZrO₂.

[0007] In another embodiment of the invention, the first catalyst mayinclude platinum. The platinum may be coated on the foam in a loading ofat least 25 grams per cubic foot of foam.

[0008] In another embodiment of the invention, the foam may have aporosity ranging from 80% to 90% and higher.

[0009] In another embodiment of the invention, the foam may include 10to 60 pores per inch.

[0010] In another embodiment of the invention, the wall flow filter mayinclude 25 to 300 cells per square inch of cross-sectional area of themonolith.

[0011] In another embodiment of the invention, the filter system mayinclude a housing. The first and second sections of the filter systemmay be carried in the housing.

[0012] Another embodiment of the invention includes a rollingregeneration diesel particulate filter trap having a first and a secondsection. The first section is positioned upstream of the second sectionwith respect to the direction of exhaust flow through the trap. Thefirst section includes a foam constructed and arranged to trap carbonparticulates in the exhaust. A first catalyst is carried by the foam topromote the conversion of NO in the exhaust flowing through the trap toNO₂. The NO₂ is used to oxidize the carbon particulates trapped by thefoam to form CO and NO. The first catalyst or a second catalyst in thefoam further promotes the oxidation of the CO to CO₂ and the oxidationof NO, generated by the reaction of NO₂ and C to generate additionalNO₂. The second section of the trap includes a wall flow filter having aplurality of through hole cells formed therein running the longitudinallength of the filter. The filter is constructed and arranged to trapparticulates in the exhaust and to promote the reaction of NO₂ and C toproduce NO and CO.

[0013] Another embodiment of the invention includes a diesel engineexhaust filter system including a catalyzed foam filter and wall flowfilter combination, wherein at least a portion of the wall flow filtersurrounds a portion of the catalyzed foam filter and so that exhaust mayflow through the catalyzed foam filter and then flow through the wallflow filter.

[0014] Another embodiment of the invention includes a diesel engineexhaust filter system having a plurality of filter combinations, andwherein each filter combination includes a catalyzed foam filter andwall flow filter, and wherein at least a portion of each wall flowfilter surrounds a portion of a catalyzed foam filter and so the exhaustmay flow through the catalyzed foam filter and then flow through thewall flow filter.

[0015] These and other objects, features and advantages will becomeapparent from the following brief description of the drawings, detaileddescription of the preferred embodiments, and appended claims anddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 illustrates a prior art diesel particulate filter system;

[0017]FIG. 2 illustrates a rolling regeneration diesel particulatefilter system according to the present invention;

[0018]FIG. 3 is a sectional view illustrating another embodiment of thepresent invention which includes a diesel engine exhaust filter systemincluding a catalyzed foam filter and wall flow filter combination;

[0019]FIG. 4 is a sectional view illustrating an alternative embodimentof the invention wherein a plurality of catalyzed foam filter and wallflow filter combinations are received in the cavity of the exhaustconduit;

[0020]FIG. 5 is a perspective view of a diesel exhaust filter systemwith a single catalyzed foam filter and wall flow filter combination;

[0021]FIG. 6 is a perspective view of a diesel exhaust filter systemwith multiple catalyzed foam filter and wall flow filter combinations;and

[0022]FIG. 7 is a graphic illustration of the pressure drop due to soot(particulate) accumulation on wall flow filters versus ceramic foams.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023]FIG. 2 illustrates a diesel engine 40 connected to a filter system42 according to the present invention. An exhaust line 44 is providedconnected at one end to the diesel engine 40 and at the other end to thefilter system 42. The filter system 42 may include a housing 46enclosing a first section 48 and a second section 50. The first section48 includes a foam 52 having a catalyst carried by the foam. The term“catalyst carried by the foam” as used herein means a catalyst coatedon, absorbed, adsorbed and/or embedded in the foam. A preferred catalystis platinum. Preferably, the foam is made from a ceramic material suchas Al₂O₃ and/or ZrO₂. The platinum is coated on the foam in a loading ofat least 25 grams per cubic foot of the foam, and more preferably 50grams or greater per cubic foot of the foam. The foam is constructed andarranged to have a porosity of at least 80% to 90% or greater. The foampreferably includes 10 to 60 pores per inch. The pores are open toprovide a tortuous flow path for the diesel exhaust flowing through thefoam. As a result, the catalyst on the foam promotes the reaction of NOin the exhaust with oxygen (also in the exhaust) to form NO₂. The foamalso is constructed and arranged to trap particulate matter such as sootand carbon-based materials in the foam. The NO₂ (present in the exhaustand generated by the reaction of NO and oxygen to form NO₂) is used tooxidize carbon (particulate matter) trapped in the foam to form NO andCO. The catalyst on the foam also promotes the oxidation of thenewly-formed NO (from the reaction of NO₂ and C) to provide anadditional source of NO₂ than that which is present in the exhaust gasesupon immediate exit from the diesel engine. The catalyst on the foamalso promotes the reaction of CO and oxygen to form CO₂ and heat.

[0024] The second section 50 of the filter system 42 includes a wallflow filter (or monolith) 54 which preferably is made from a ceramicmaterial and includes a plurality of through hole cells formed thereinrunning the longitudinal length of the filter 54. The filter 54 isconstructed and arranged to trap particulate matter in the exhaust andto promote the reaction of NO₂ and carbon (particulate matter) toproduce NO and CO. Preferably, the filter 54 includes at least 25 to 300cells per square inch of a cross-sectional area of the monolith. Theeffluent line 56 exiting the filter system 42 includes NO, CO, NO₂ andCO₂. Additional filtering and purification operations may be conductedon the effluent 56 by downstream components (not shown).

[0025]FIG. 3 is a sectional view illustrating another embodiment of thepresent invention which includes a diesel engine exhaust filter system100 including a catalyzed foam filter 110 and wall flow filter 116combination. The term “catalyzed foam filter” as used herein means afoam having a catalyst coated on, absorbed, adsorbed and/or embedded inthe foam. The diesel engine exhaust system 100 includes an exhaustconduit 102 which naturally includes a cavity 104 through which exhaustfrom a diesel combustion engine flows from the combustion engine throughthe exhaust conduit 102 and is eventually expelled to the atmosphere.The system 100 includes the catalyzed foam filter 110 having open pores(as described above) and the wall flow filter 116 housed in the cavity104 of the exhaust conduit 102. The wall flow filter 116 is preferably asingle cell structure and includes a porous wall 118 that is spaced adistance from an inner surface 103 of the conduit 102. Preferably, thecatalyzed foam filter 110 and the wall flow filter 116 are bothsupported by a separator 106 that extends between inner surfaces 103 ofthe conduit 102. Preferably, the separator 106 includes an opening 107therethrough exposing a front face 108 of the catalyzed foam filter 110so that exhaust gases may flow through the opening 107 in the separator106 and into the foam 110. The exhaust gases flow in the direction ofarrows 121 from the diesel combustion engine flow towards the front face108 of the catalyzed foam filter 110, through the catalyzed foam filter110, and through a porous wall 118 of the wall flow filter 116 asindicated by arrows 122. Particulates are trapped by the catalyzed foamfilter 110, and by the wall flow filter 116 in a space 120 between thecatalyzed foam filter 110 and the wall 118 of the wall flow filter 116.The porous wall 118 may be any suitable material such as a ceramic,including, for example, alumina with 10 to 20 micron pore size and aporosity of 40% or greater. The wall 118 may have a thickness of 0.25 mmto 1 mm, and preferably 0.5 mm. The catalyzed foam filter 110 includes alongitudinal side (or sides) edge or peripheral edge 112 and a rear face104. The side edge 112 and rear face 104 are each spaced a distance ofabout 2 mm to 5 mm from the porous wall 118 of the wall flow filter 116to provide the space 120 therebetween for the accumulation ofparticulates in the diesel exhaust gas. Preferably, at least a portionof the wall flow filter 116 surrounds a portion of the catalyzed foamfilter 110. In a preferred embodiment, the wall flow filter 116surrounds the catalyzed foam filter 110 along at least a portion of thelongitudinal side edge 112 and the rear face 104 of the catalyzed foam110. However, it is also contemplated that a solid cap (not shown) maybe provided adjacent the rear face 104 to force the flow of exhaust gasout of the side edge 112 and not out of the rear face 104. A perspectiveview of a diesel exhaust filter system with a single catalyzed foamfilter 110 and wall flow filter 116 combination is shown in FIG. 5.

[0026]FIG. 4 is a sectional view illustrating an alternative embodimentof the invention wherein a plurality of catalyzed foam filter 110 andwall flow filter 116 combinations are received in the cavity 104 of theexhaust conduit 102. Preferably, each of the catalyzed foam filter 110and wall flow filter 116 combinations are supported by the separator 106that has a plurality of openings 107 therethrough, one opening 107 foreach of the combinations (110 and 116). A perspective view of a dieselexhaust filter system with multiple catalyzed foam filter 110 and wallflow filter 116 combinations is shown in FIG. 6.

[0027]FIG. 7 is a graphic depiction of the pressure drop versusparticulate mass loading for a 100 cells per inch wall flow filter, a200 cells per inch wall flow filter and a ceramic foam having a porosityranging from 80% to 90% and about 10 to 60 pores per square inch. Aswill be appreciated, a ceramic foam used according to the presentinvention has a pressure drop of about {fraction (1/10)} or less thanwall flow filters. This allows the present invention to incorporate afoam coated with a catalyst such as platinum thereon to be used to trapparticulate matter, thus reducing the particulate loading on thedownstream wall flow filter. Due to the tortuous flow path of theexhaust through the foam, NO₂ is generated in addition to the NO₂present in the exhaust gas from the diesel engine. The additional NO₂helps to oxidize carbon trapped in the foam and carbon trapped by thedownstream wall flow monolith. As a consequence, the foam and thedownstream wall flow monolith do not have to be cleaned as often toreduce particulate as prior art systems.

1. A rolling regeneration diesel particulate filtering process thatreuses NO produced in the process to generate additional amounts of NO₂,comprising: flowing diesel engine combustion exhaust through a filtersystem comprising a first section and a second section, and wherein thefirst section is positioned upstream of the second section with respectto the flow direction of the exhaust gas, and wherein the first sectionincludes a foam constructed and arranged to trap carbon-basedparticulates in the exhaust, and a first catalyst carried by the foam topromote the conversion of NO in the exhaust from the diesel engine toNO₂, and to promote the reaction of at least a portion of theparticulates trapped in the foam with NO₂ to form CO and NO, and whereinthe first catalyst carried by the foam further promotes the oxidation ofCO to CO₂, and the oxidation of NO, generated by the reaction of NO₂with carbon, to generate additional NO₂, and wherein the second sectionincludes a wall flow filter having at least one through hole cell formedtherein running the longitudinal length of the wall flow filter, and thewall flow filter being constructed and arranged to trap particulates inthe exhaust and to promote the reaction of NO₂ and C to produce NO andCO.
 2. A process as set forth in claim 1 wherein the foam comprises aceramic foam including Al₂O₃.
 3. A process as set forth in claim 2wherein the ceramic foam further includes ZrO₂.
 4. A process as setforth in claim 1 wherein the foam comprises a ceramic foam includingZrO₂.
 5. A process as set forth in claim 1 wherein the first catalystcomprises platinum.
 6. A process as set forth in claim 1 wherein thefirst catalyst comprises platinum carried by the foam in a loading of atleast 25 grams per cubic foot of foam.
 7. A process as set forth inclaim 1 wherein the foam has a porosity ranging from 80% to 90%.
 8. Aprocess as set forth in claim 1 wherein the foam includes 10 to 60 poresper inch.
 9. A process as set forth in claim 1 wherein the wall flowfilter includes 25 to 300 cells per square inch of cross-sectional areaof the wall flow filter.
 10. A process as set forth in claim 1 whereinthe filter system further includes a housing, and wherein the first andsecond sections are carried in the housing.
 11. A rolling regenerationdiesel particulate filter system comprising: a first section and asecond section, and wherein the first section is positioned upstream ofthe second section, and wherein the first section includes a foamconstructed and arranged to trap carbon-based particulates in dieselengine exhaust flowing through the filter, and a first catalyst carriedby the foam to promote the conversion of NO in the diesel engine exhaustto NO₂, and the first catalyst being designed to promote the reaction ofNO₂ with at least a portion of the carbon-based particulates trapped bythe foam to form CO and NO, and wherein the first catalyst carried bythe foam further promotes the oxidation of CO to CO₂, and the oxidationof NO, generated by the reaction of NO₂ with carbon, to generateadditional NO₂, and wherein the second section includes a wall flowfilter having at least one through hole cell formed therein running thelongitudinal length of the wall flow filter, and the wall flow filterbeing constructed and arranged to trap particulates in the diesel engineexhaust flowing through the wall flow filter and to promote the reactionof NO₂ and C to produce NO and CO.
 12. A system as set forth in claim 11wherein the foam comprises a ceramic foam including Al₂O₃.
 13. A systemas set forth in claim 12 wherein the ceramic foam further includes ZrO₂.14. A system as set forth in claim 11 wherein the foam comprises aceramic foam including ZrO₂.
 15. A system as set forth in claim 11wherein the first catalyst comprises platinum.
 16. A system as set forthin claim 11 wherein the first catalyst comprises platinum carried by thefoam in a loading of at least 25 grams per cubic foot of foam.
 17. Asystem as set forth in claim 11 wherein the foam has a porosity rangingfrom 80% to 90%.
 18. A system as set forth in claim 11 wherein the foamincludes 10 to 60 pores per inch.
 19. A system as set forth in claim 11wherein the wall flow filter includes 25 to 300 cells per square inch ofcross-sectional area of the wall flow filter.
 20. A system as set forthin claim 11 further comprising a housing, and wherein the first andsecond sections are carried in the housing.
 21. A rolling regenerationdiesel particulate filtering process that reuses NO produced in theprocess to generate additional amounts of NO₂, comprising: flowingdiesel engine combustion exhaust through a first section of a filtersystem and thereafter flowing the exhaust through a second section ofthe filter system, and wherein the first section includes a foamconstructed and arranged to trap carbon-based particulates in theexhaust, and a first catalyst carried by the foam to promote theconversion of NO in the exhaust from the diesel engine to NO₂, and topromote the reaction of at least a portion of the particulates trappedin the foam with NO₂ to form CO and NO, and wherein the first catalystcarried by the foam further promotes the oxidation of CO to CO₂, and theoxidation of NO, generated by the reaction of NO₂ with carbon, togenerate additional NO₂, and wherein the second section includes a wallflow filter having at least one through hole cell formed therein runningthe longitudinal length of the wall flow filter, and the wall flowfilter being constructed and arranged to trap particulates in theexhaust and to promote the reaction of NO₂ and C to produce NO and CO.22. A diesel engine exhaust filter system comprising: a catalyzed foamfilter and wall flow filter combination, wherein at least a portion ofthe wall flow filter surrounds a portion of the catalyzed foam filterand so that exhaust may flow through the catalyzed foam filter and thenflow through the wall flow filter.
 23. A system as set forth in claim 22further comprising a conduit having a cavity defined by an inner surfaceand wherein the combination is received in the cavity.
 24. A system asset forth in claim 23 wherein the catalyzed foam filter includes a frontface, and further comprising a separator connected to the inner surfaceand the separator having an opening therethrough, and wherein thecombination is supported by the separator so that the opening exposesthe front face of the catalyzed foam filter.
 25. A system as set forthin claim 22 wherein the catalyzed foam filter includes a side edge and arear face and wherein the wall flow filter surrounds at least a portionof the side edge.
 26. A system as set forth in claim 25 wherein the wallflow filter surrounds the rear face of the catalyzed foam filter.
 27. Asystem as set forth in claim 22 wherein the wall flow filter is a singlecell wall flow filter.
 28. A system as set forth in claim 25 wherein thewall flow filter comprises a porous wall spaced a distance from the sideedge.
 29. A system as set forth in claim 28 wherein the porous wall isspaced a distance from the rear face of the catalyzed foam filter.
 30. Adiesel engine exhaust filter system comprising: a plurality of filtercombinations, and wherein each filter combination includes a catalyzedfoam filter and wall flow filter, and wherein at least a portion of eachwall flow filter surrounds a portion of a catalyzed foam filter and sothe exhaust may flow through the catalyzed foam filter and then flowthrough the wall flow filter.
 31. A system as set forth in claim 30further comprising a conduit having a cavity defined by an inner surfaceand wherein each combination is received in the cavity.
 32. A system asset forth in claim 31 wherein each catalyzed foam filter includes afront face, and further comprising a separator connected to the innersurface and the separator having a plurality of openings therethrough,and wherein each opening is constructed and arranged to expose the frontface of one of the catalyzed foam filters.
 33. A system as set forth inclaim 30 wherein each catalyzed foam filter includes a side edge andwherein one of the wall flow filters surrounds at least a portion of theside edge.
 34. A system as set forth in claim 33 wherein each catalyzedfoam filter further includes a rear face and wherein the wall flowfilter surrounds the rear face of the catalyzed foam filter.